Injection Molded Cold-Expansion Compression Collar

ABSTRACT

A compression collar is manufactured for use in reinforcing an interference fit between an end of a pipe and a fitting. A precursor form is injection molded using a cold-expansion material. The precursor form has a tubular body with an initially closed axial end and a bore that is initially blind formed in the other axial end. Material is removed from the initially closed axial end of the tubular body of the precursor form to form an opening in the initially closed axial end that connects to the bore thereby forming the compression collar. The opening has an inner periphery with a profile in axial cross section that is different than any profile in axial cross section of an inner periphery of the bore. The collar formed may lack knitlines and may include tabs formed during the removal step which help to position the collar on a pipe.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 62/383,001 entitled “Injection Molded Cold-ExpansionCompression Collar” filed Sep. 2, 2016, the contents of which areincorporated by reference herein in its entirety for all purposes.

STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND

This disclosure relates, in general, to improvements in cold-expansioncompression collars or reinforcing rings for making leak-free tubeconnections. More particularly, this disclosure relates to a method formaking compression collars for cold-expansion tubing connections, suchas in piping made from polyolefin, polyethylene, cross-linkedpolyethylene, PEX-a, PEX-b, PEX-c, PERT, or any other similar material.

Cold-expansion tubing has been used in plumbing applications for decadesin Europe and now increasingly in the United States. The principlebehind its operation is to manufacture a hollow, tubular material andimbue it with shape memory properties (e.g., through cross-linking,irradiation, steam, etc.) such that when the tubing is stretched ordeformed, the tubing returns to the shape set in its memory during themanufacturing process. In use, cold-expansion tubing can be widened orbelled at its end and allowed to shrink back to its original shape aftermere moments at room temperature. The elastic forces within thecold-expansion tubing material can be applied to any object thatinterferes with the cold-expansion tubing as it returns to its originalshape. Thus, cold-expansion tubing can form interference fits or jointswith fittings, other piping, etc.

It is known in the state of the art that such a cold expansion fittingconnection between a pipe and a fitting may be further strengthen byplacing a compression collar around the end of the pipe or tubing priorto cold expansion. See e.g., U.S. Pat. No. 5,735,554. By forming boththe compression collar and the pipe from a cold-expansion material andby placing the compression collar at the axial end of the pipe, both thecollar and pipe can be expanded simultaneously, moved over a fitting,and then allowed to return to substantially the same size and shape atroom temperature. The addition of compression collar provides additionalcompressive forces beyond that of just the pipe to create a better sealfor the connection and reinforces the interference fit between the pipeand the fitting over which the pipe is received.

However, more so than just the pipe, the compressive collar is subjectedto high loads under elastic deformation. Thus, there is a need toattempt to develop compressive collars having more robust structure andincreased strength.

SUMMARY

The present disclosure is directed to an improved method ofmanufacturing compression collars or reinforcing rings for acold-expansion joining system using injection molding. While injectionmolding has been used to produce compression collars (see e.g., U.S.Patent Application Publication No. 2008/0315579), such conventionalinjection molding has been known to introduce knitlines. Knitlines arelines within the injection molded part, often not visible by the nakedeye, at which two fronts of material have flowed together during theinjection molding process. Such knitlines form weak regions which aremore prone to failure than otherwise homogeneous areas of the injectionmolded collar. To reinforce these lines of inherent weakness, it hasbeen proposed to thicken the wall at the knitlines. See again, U.S.Patent Application Publication No. 2008/0315579.

Disclosed herein is a method of eliminating knitlines altogether in aninjection molded compression collar. This elimination of knitlines hasthe clear advantage of strengthening the part (in comparison to acomponent having a similar geometry, but with knitlines) and further hasthe advantage of eliminating thick wall sections which has been proposedby others, thereby reducing material.

To mold a compression collar without knitlines, a continuous gate isutilized at the axial end of a precursor form from which the compressioncollar will be formed. As such, the injected material flows from thepoint or points of injection on the axial end, radially outward to thecylindrical walls, and then down the cylindrical walls without theinjected material ever flowing into itself. Thus, this continuous gateinitially forms a solid wall or capped end at one axial end of thecollar which would otherwise be a substantially hollow cylinder. Oncethe precursor form is injection molded, the excess gate material isremoved from the axial end. The removal of excess gate material can beaccomplished, for example, through a trimming or punching operation.While it is possible to remove the gate entirely, in some preferredforms, some amount of the axial end wall remains to function aspositioning stops or tabs thereby providing a locating mechanism for thecompression collar when placed on the end of the piping.

According to one aspect, a method is disclosed for manufacturing acompression collar for reinforcing an interference fit between an end ofa pipe and a fitting. A precursor form is injection molded using acold-expansion material, in which the precursor form comprises a tubularbody with an initially closed axial end and a bore that is initiallyblind formed in the other axial end. Material is removed from theinitially closed axial end of the tubular body of the precursor form toform an opening in the initially closed axial end that connects to thebore thereby forming the compression collar. The opening has an innerperiphery with a profile in axial cross section that is different thanany profile in axial cross section of an inner periphery of the bore.

In many forms, the cold-expansion material may be one or more of apolyolefin, cross-linked polyolefin, polyethylene, cross-linkedpolyethylene, PEX, PEX-a, PEX-b, PEX-c, and PERT.

In some forms, because of the manner of injection molding and removedmaterial, the compression collar may include no knitlines. It iscontemplated that the injection point(s) may be located at the initiallyclosed axial end, for example at the central axis, such that theinjected material flows radially outward along the initially closed endand then axially downward along the tubular sidewalls, such that thefront of the injected material never substantially flows into itself toform a knitline. In some forms, the step of removing material from theinitially closed axial end of the tubular body of the precursor form toform an opening may involves removing any injection points on theprecursor form used in the step of injection molding the precursor form.

Although various ways of removing material from the initially closedaxial are contemplated, in some forms the step of removing material fromthe initially closed axial end of the tubular body of the precursor formto form an opening in the initially closed axial end may involvepunching.

In some forms, the step of removing material from the initially closedaxial end of the tubular body of the precursor form to form an openingin the initially closed axial end may form one or more positioning tabsin the inner periphery of the opening. Such position tabs might beuseful to position the compression collar on the end of the pipe onwhich it will be received so that the collar is not, for example, slidpast the axial end of the pipe. If there are multiple positioning tabs,then those tabs may be located at even intervals around the innerperiphery.

It is contemplated that, in some forms, the opening may have an innerperiphery with a profile in axial cross section that matches, in part,an adjacent profile in axial cross section of an inner periphery of thebore with a non-matching part of the profiles providing at least onepositioning tab in the inner periphery of the opening.

In some forms, the compression collar may further include a supportingextension or “tail” on the axial end of the compression collar oppositethe axial end having the opening that is removed. Such a supportingextension may be configured to reinforce a thinned section of the pipepast the fitting. The supporting extension may have different shapes.For example, in some forms, the supporting extension mat tapers as itextends away from the opening (meaning that the wall thicknessdecreases). In some other forms, the supporting extension may have arelatively constant wall thickness, although this wall thickness maystill be less than the wall thickness of the main portion of thecompression collar.

In some forms, the method may further involve, during injection molding,forming flat surfaces on the inner periphery of the bore of thecompression collar that are parallel to a central axis of thecompression collar. These flat surfaces may be configured to be tangentto a radially-outward facing surface of the pipe around which thecompression collar will be received during its attachment to the end ofthe pipe in forming a connection.

In some forms, the method may further include forming a chamfered edgeor a curved corner with a radius of curvature in the bore at the axialend of the bore that is opposite the axial end in which opening isremoved.

According to another aspect, a compression collar is disclosed forreinforcing an interference fit between an end of a pipe and a fitting.The compression collar includes a tubular body formed by injectionmolding a cold-expansion material in which the tubular body has a boreextending axially therethrough and a removed opening on oneinitially-closed axial end of the tubular body in which the removedopening connects to the bore. The opening has an inner periphery with aprofile in axial cross section that is different than any profile inaxial cross section of an inner periphery of the bore.

In some forms, the cold-expansion material may be one or more of apolyolefin, cross-linked polyolefin, polyethylene, cross-linkedpolyethylene, PEX, PEX-a, PEX-b, PEX-c, and PERT.

In some forms, the compression collar includes no knitlines and noresidual injection points from injection molding.

In some forms, the compression collar may further include flat surfaceson the inner periphery of the bore that are parallel to a central axisof the compression collar such that the flat surfaces are configured tobe tangent to a radially-outward facing surface of the pipe around whichthe compression collar is to be received. In some forms, the removedopening may include positioning tabs and there may be as many flatsurfaces on the inner periphery as there are positioning tabs.

In some forms, the compression collar may further include a supportingextension or “tail” on the axial end of the compression collar oppositethe axial end having the opening that is removed. Such a supportingextension may be configured to reinforce a thinned section of the pipepast the fitting. The supporting extension may have different shapes.For example, in some forms, the supporting extension mat tapers as itextends away from the opening (meaning that the wall thicknessdecreases). In some other forms, the supporting extension may have arelatively constant wall thickness, although this wall thickness maystill be less than the wall thickness of the main portion of thecompression collar.

In some forms, the compression collar may further include a chamferededge or a curved corner with a radius of curvature in the bore at theaxial end of the bore that is opposite the removed opening.

In some forms of the compression collar, the inner periphery of theremoved opening includes one or more positioning tabs in which thepositioning tab(s) is/are configured to axially position the compressioncollar on an end of a pipe.

In some forms, the removed opening may have an inner periphery with aprofile in axial cross section that matches, in part, an adjacentprofile in axial cross section of an inner periphery of the bore andwith a non-matching part of the profiles defining one or morepositioning tabs in the inner periphery of the removed opening.

These and still other advantages of the invention will be apparent fromthe detailed description and drawings. What follows is merely adescription of some preferred embodiments of the present invention. Toassess the full scope of the invention the claims should be looked to asthese preferred embodiments are not intended to be the only embodimentswithin the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a precursor form with a closed end frominjection molding that is further manufactured into a collar.

FIG. 1B is a side plan view of the precursor form of FIG. 1A.

FIG. 1C is a cross-sectional side view of the precursor form of FIG. 1Ataken through line 1C-1C of FIG. 1B.

FIG. 2A is a perspective view of the compression collar form from theprecursor form of FIGS. 1A-1C after a material removing operation.

FIG. 2B is a side plan view of the compression collar of FIGS. 2A.

FIG. 2C is a front axial plan view of the compression collar of FIGS.2A.

FIG. 3A is a perspective view of a connection made using anothercompression collar, after the collar has been put on the end of a pipe,the pipe and collar have been cold expanded and placed over a fitting,and the pipe and collar have compressed around the fitting to form aseal.

FIG. 3B is a plan side of the connection of FIG. 3A.

FIG. 3C is a front axial end plan view of the connection of FIG. 3A.

FIG. 3D is a cross-sectional side view of the connection of FIG. 3A,taken through line 3D-3D of FIG. 3C.

FIG. 4A is a perspective view of yet another compression collar in whichthe central bore has flats.

FIG. 4B is a front axial end plan view of the collar of FIG. 4A.

FIG. 4C is a cross-sectional side view of the compression collar of FIG.4A, in which the section is taken through line 4C-4C of FIG. 4B.

FIG. 4D is a side plan view of the compression collar of FIG. 1A.

FIG. 4E is a rear axial end plan view of the collar in FIG. 4A.

FIG. 4F is a detailed view of the compression collar of FIG. 4A taken inarea 4F-4F of FIG. 4E, looking into the rear bore end to further impressthe positioning of the flat relative to the positioning tab.

DETAILED DESCRIPTION

FIGS. 1A-1C show one example embodiment of a precursor form 100 which isfurther processed to form a compression collar 200 which may also bereferred to as a reinforcing ring. It is noted that similar featuresbetween the precursor form 100 and the collar 200 (which is effectivelya further manufactured form of the precursor form 100) will have similarreference numbers, except that the leading “1” or “2” will be alter thereference numbers from the 100 series to the 200 series.

Looking first at FIGS. 1A-1C, the precursor form 100 is shown as it hasbeen injection molded. The precursor form 100 may be formed fromcold-expansion material comprising polyolefin, cross-linked polyolefin,polyethylene, cross-linked polyethylene, PEX, PEX-a, PEX-b, PEX-c, PERT,and/or any other material exhibiting memory properties such that at roomtemperature the material may be stretched and immediately or shortlythereafter allowed to shrink back down to the material's previous shapebefore the stretching operation. Materials with this property may beadvantageously used in creating interference or frictional fits orjoints because of the forces exerted by the material on any object,which is larger than the material's normal shape, and over which thematerial is stretched, placed, and allowed to shrink. Thus, depending onthe amount of stretching and the thickness of the material, strongsqueezing forces exerted by the material on an object may cause theobject to remain in place and resist becoming dislodged by other forces.Additionally, the high elongation before break or flexibility of thematerial allows for elastic stretching rather than cracking or tearing.

The precursor form 100 may have an overall tubular shape with acylindrical bore formed through one end of the cylindrical shape with aninitially closed axial end 108 at the opposing end, having beeninjection molded with an axial length 102, an inner diameter 104, and anouter diameter 106. This makes the bore initially a blind bore. Thecylindrical bore of the precursor form 100 is formed in the one end ofthe cylindrical shape that will be slid over the end of a section ofpipe in use. In order to facilitate sliding the final collar 200 overthe pipe, an end chamfer 120 (as illustrated in FIGS. 2B and 2C) may beformed at the opened axial end of the bore of the precursor preform 100.Alternatively, the end chamfer 120 may be formed as a curved cornerhaving a certain radius of curvature. The radius of curvature may vary.The closed axial end 108 is located at the axial opposing end of theprecursor form 100 which corresponds to the axial end that will bearranged closest to the end of the piping in use.

The desired axial length 102 of the precursor form 100 may be based onthe inner and outer diameters 104, 106 and/or the intended use of thecompression collar 200 manufactured from the precursor form 100. Forexample, the inner diameter 104 of the precursor form 100 may range fromabout a ¼″ to about 6″ in order to just fit or slide over the outerdiameter of standard cold-expansion pipe for residential or commercialapplications. Additionally, the compression collar 200 resultingfabricated from the precursor form 100 may be certified under the ASTMF1960 standard and may be used with standard manual pipe expanders oreven automatic expander power tools, such as the M12™ 12V CordlessLithium-Ion ProPEX® Expansion Tool by Milwaukee Electric Tool®, forexample.

The formation of the closed axial end or continuous gate 108 at the endof the precursor form 100 during injection molding may be facilitated byusing a fan gate or other similar gate, such as a sprue gate orsubmarine gate, for example. A fan gate injection point 110 ispreferably located at the center of the closed end 108 correspondingwith the central axis of the precursor form 100. The mold for theprecursor form 100 of the compression collar 200 may be arranged suchthat the closed end 108 is located at the top. In this way, theinjection molding material flowing through the central gate injectionpoint 110 has a single front that flows radially outward and thensubstantially uniformly down and around the whole mold to fill in thetubular-shaped sidewall of the precursor form 100. Because there is onlyone material front flowing around and down into the mold, no knitlinesare formed where the flowing materials meet. This advantageouslyeliminates any potential weak points in the final compression collar 200that may tear when subjected to expanding forces or that may otherwisehave to be reinforced.

After molding, the material comprising the closed axial end 108 of theprecursor form 100 is then removed to form an opening (i.e., a removedopening) that is connected to the bore. In order to remove the materialfrom the closed axial end 108 of the precursor form 100, cutting,trimming, punching, or similar known operations may be performed. As anon-limiting example, material may be removed or punched from theinitially closed axial end 108 of the precursor form 100 by using a dieon a punch press. The die is shaped to match the material to be removedfrom the closed end 108.

Rather than remove the closed end 108 material completely, some materialmay be left to function as positioning tabs or stops 212, as seen inFIGS. 2A-2C. The positioning tabs 212 advantageously position thecompression collar 200 on the piping or fitting over which thecompression collar 200 is to be placed. Thus, the thickness of thepositioning tabs 212 (i.e., the axial thickness of the closed end 108)may be based on the inner diameter 204 and/or the outer diameter 206 ofthe compression collar 200. Alternatively or additionally, the thicknessof the positioning tabs 212 may be based on a thickness and/or outerdiameter of the pipe and/or fitting over which the compression collar200 is to be placed. For example, the positioning tabs 212 may be about1/96″ up to about 1/16″ thick for fitting over pipe with a ½″ outerdiameter.

The positioning tabs 212 may vary in height (measured axially) and arenot limited to the embodiment shown in FIGS. 2A-2C. The height of thepositioning tabs 212 may be based on the efficiency of the materialremoval operation and/or the cost of materials. Additionally, the heightof the positioning tabs 212 may be based on the nominal inner diameter204 and/or the outer diameter 206 of the compression collar 200.Alternatively or additionally, the height of the positioning tabs 212may be based on a thickness and/or outer diameter of the piping and/orfitting over which the compression collar 200 is to be placed.

Similarly to the height, the shape of the positioning tabs 212 may varyand are not limited to the embodiment shown in FIGS. 2A-2C. The shape ofthe positioning tabs 212 may be based on the efficiency of the materialremoval operation and/or the cost of materials. For example, thepositioning tabs 212 may taper to a point moving toward the center ofthe compression collar 200. As another non-limiting example, thepositioning tabs 212 may remain substantially the same width movingtoward the center of the compression collar 200. The positioning tabs212 may each have a different shape and/or alternate shapes. Forexample, there may be one positioning tab with a tapering shape and theremaining positioning tabs have a more rectangular shape such that thepositioning tab with the tapering shape marks one side of thecompression collar for orientation, alignment, and/or registrationpurposes.

The positioning tabs 212 may vary in width from the embodiment shown inFIGS. 2A-2C. The width of the positioning tabs 212 may be based on thenumber of positioning tabs 212 to be formed by the material removaloperation. For example, a larger width may be employed for a lowernumber of positioning tabs and/or a smaller width may be employed for ahigher number of positioning tabs. The positioning tabs may differ fromeach other in widths as described above with respect to shape variationsof the positioning tabs in the compression collar.

As an alternative to the plurality of positioning tabs 212, there may beonly one positioning tab. The single positioning tab may vary in widthfrom the positioning tabs 212 shown in FIGS. 2A-2C. For example, thesingle positioning tab may have a width that extends around about aquarter or half of the circumference of the inner bore of thecompression collar 200. As another non-limiting example, the singlepositioning tab may extend around the majority of the circumference ofthe inner bore of the compression collar.

FIGS. 3A-3D show a connection 300 formed between another compressioncollar 400 that has been placed over a pipe 500 which are collectivelyslid over a fitting 600. Collar 400 is identical to collar 200, exceptthat it further has a supporting extension 422 or “tail.” As best seenin FIG. 3D, the compression collar 400 is shown after being placed overthe end of a section of pipe 500, being coaxially cold expanded with thepipe 500, being placed over the fitting 600 (i.e., axially slid onto thefitting 600 is a still-expanded condition), and being allowed to shrinkback over a fitting 600.

The compression collar 400 includes positioning tabs 412 as well as asupporting extension 422 that extends beyond a nominal length 406 of thecompression collar 400. The supporting extension 422 may taper in wallthickness moving from the region of nominal length 406 toward the end.Alternatively, the supporting extension 422 may maintain the same wallthickness.

In production, the supporting extension 422 may be incorporated into thecompression collar 400 during injection molding, as described above. Thecombined lengths of the nominal length 406 of the compression collar 400and the supporting extension 422 may be based on the desired wallthickness and the inner and outer diameters of the compression collar400, the intended use of the compression collar 400, and/or the type andinsertion length of the fitting 600.

The supporting extension 422 may advantageously provide additionalstrength and external support for an area 316 of the connection 300where the pipe 500 meets the axial end of the fitting 600. In this area316, the wall of the pipe 500 may be stretched or thinned due to theexpansion joining process. Thus, providing the compression collar 400with the supporting extension 220 surrounding this area 316 may reducethe hydrostatic stress in the wall of the pipe 500, increasing thepressure capability of the pipe 500 and bringing the margin of safetyfor practical applications back up to at least the original designlimits. In this way, the compression collar 400 can provide not onlyextra compressive force at the sealing interface on the fitting 600 toprevent the connection 300 from leaking, but also additional externalsupport for the pipe 500 in the area 316 of potential weakening justbeyond the inserted length of the fitting 600.

FIGS. 4A-4F show yet another exemplary embodiment of a compressioncollar 700, which is similar to collar 200 (where the reference numbersin the 700 series again correspond to the reference numbers from the 200series) but in which there are flats 714 form in the radially inwardfacing surface of the bore. The compression collar 700 may be injectionmolded and as such is shown after the material removing operationdescribed above with respect to the precursor form 100 and collar 200.The compression collar 700 has an axial length 702, an inner diameter704, and an outer diameter 706. The compression collar 700 includespositioning tabs 712, as described above, that prevent the end of asection of piping from sliding completely through the collar 700. Theend of the compression collar 700 that slides over the end of the pipingmay include chamfering 720 formed into the inner diameter 704. Thischamfering 720 may facilitate initial entry of the piping into the innerdiameter 704 of the compression collar 700. Alternatively, thechamfering 720 may be formed as a curved corner having a certain radiusof curvature. The radius of curvature may vary.

Additionally included on the compression collar 700 is one or more flatsurfaces or strips 714 that are axially tangent to the pipe over whichthe collar 700 is placed in use. These flat surfaces 714 may be formedon the inner wall of the cylindrical bore during the injection moldingprocess. The flat surfaces 714 advantageously provide a slight amount offriction for a lightly snug fit between the compression collar 700 andthe radially outward facing surface of the pipe that will keep thecollar 700 from sliding off the pipe prior to expansion. A furtheradvantage of the flat surfaces 714 is that they are parallel with thecentral axis of the compression collar 700 such that the same slightamount of friction is applied evenly all along the end of the section ofpipe which is inserted into the collar 700.

The flat surfaces 714 may vary in width and are not limited to theembodiment shown in FIGS. 4A-4F. The width of the flat surfaces 714 maybe based on the inner diameter 704 and/or the outer diameter 706 of thecompression collar 700. Alternatively or additionally, the width of theflat surfaces 714 may be based on a thickness and/or outer diameter ofthe pipe and/or fitting over which the compression collar 700 is to beplaced. The width of the flat surfaces 714 may be based on the number offlat surfaces 714. For example, a larger width may be employed for alower number of flat surfaces 714 and/or a smaller width may be employedfor a higher number of flat surfaces 714. The flat surfaces 714 may eachhave a different width and/or alternate widths. For example, there maybe one flat surface 714 with a larger width and the remaining flatsurfaces 714 have smaller widths such that the flat surface 714 with thelarger width marks one side of the compression collar 700 fororientation, alignment, and/or registration purposes.

The number of flat surfaces 714 may be based on the width of the flatsurfaces 714, the inner and outer diameters 704, 706 of the compressioncollar 700, the outer diameter of the pipe over which the collar 700 isto be placed, and/or the number of positioning tabs 712. The flatsurfaces 714 may be evenly distributed around the inner diameter 704 ofthe compression collar 700 or alternatively distributed unevenly. Theflat surfaces 714 may be aligned and/or misaligned with the positioningtabs 712. As an alternative to the plurality of flat surfaces 714, theremay be only one flat surface. The single flat surface may vary in widthfrom the flat surfaces 314 shown in FIGS. 4A-4F.

It should be appreciated that various other modifications and variationsto the preferred embodiments can be made within the spirit and scope ofthe invention. Therefore, the invention should not be limited to thedescribed embodiments. To ascertain the full scope of the invention, thefollowing claims should be referenced.

What is claimed is:
 1. A method for manufacturing a compression collarfor reinforcing an interference fit between an end of a pipe and afitting, the method comprising the steps of: a. injection molding aprecursor form using a cold-expansion material, wherein the precursorform comprises a tubular body with an initially closed axial end and abore that is initially blind formed in the other axial end; and b.removing material from the initially closed axial end of the tubularbody of the precursor form to form an opening in the initially closedaxial end that connects to the bore thereby forming the compressioncollar; wherein the opening has an inner periphery with a profile inaxial cross section that is different than any profile in axial crosssection of an inner periphery of the bore.
 2. The method of claim 1,wherein the cold-expansion material is at least one of polyolefin,cross-linked polyolefin, polyethylene, cross-linked polyethylene, PEX,PEX-a, PEX-b, PEX-c, and PERT.
 3. The method of claim 1, wherein thecompression collar includes no knitlines.
 4. The method of claim 1,wherein the step of injection molding involves injecting allcold-expansion material at an injection location positioned on theinitially closed axial end, such that the cold-expansion material flowsradially outward on the initially closed axial end and then axialdownward into generally tubular sidewalls of the tubular body withoutthe material front flow into itself or another material front during thestep of injection molding.
 5. The method of claim 1, wherein the step ofremoving material from the initially closed axial end of the tubularbody of the precursor form to form an opening involves removing anyinjection points on the precursor form used in the step of injectionmolding the precursor form.
 6. The method of claim 1, wherein the stepof removing material from the initially closed axial end of the tubularbody of the precursor form to form an opening in the initially closedaxial end involves punching.
 7. The method of claim 1, wherein the stepof removing material from the initially closed axial end of the tubularbody of the precursor form to form an opening in the initially closedaxial end forms at least one positioning tab in the inner periphery ofthe opening.
 8. The method of claim 7, wherein the at least onepositioning tab includes a plurality of positioning tabs.
 9. The methodof claim 8, wherein the plurality of positioning tabs are located ateven intervals around the inner periphery.
 10. The method of claim 1,wherein the compression collar further comprises a supporting extensionon the axial end of the compression collar opposite the opening that isremoved, the supporting extension being configured to reinforce athinned section of the pipe past the fitting.
 11. The method of claim10, wherein the supporting extension tapers as it extends away from theopening.
 12. The method of claim 1, further comprising, during injectionmolding, forming flat surfaces on the inner periphery of the bore of thecompression collar that are parallel to a central axis of thecompression collar such that the flat surfaces are configured to betangent to a radially-outward facing surface of the pipe around whichthe compression collar is received.
 13. The method of claim 1, furthercomprising the step of forming a chamfered edge in the bore at the axialend of the bore that is opposite the axial end in which opening isremoved.
 14. The method of claim 1, further comprising the step offorming a curved corner with a radius of curvature in the bore at theaxial end of the bore that is opposite the axial end in which opening isremoved.
 15. The method of claim 1, wherein the opening has an innerperiphery with a profile in axial cross section that matches, in part,an adjacent profile in axial cross section of an inner periphery of thebore with a non-matching part of the profiles providing at least onepositioning tab in the inner periphery of the opening.
 16. A compressioncollar for reinforcing an interference fit between an end of a pipe anda fitting, the compression collar comprising: a tubular body formed byinjection molding a cold-expansion material, the tubular body having abore extending axially therethrough and a removed opening on oneinitially closed axial end of the tubular body in which the removedopening connects to the bore; wherein the opening has an inner peripherywith a profile in axial cross section that is different than any profilein axial cross section of an inner periphery of the bore.
 17. Thecompression collar of claim 16, wherein the cold-expansion material isat least one of polyolefin, cross-linked polyolefin, polyethylene,cross-linked polyethylene, PEX, PEX-a, PEX-b, PEX-c, and PERT.
 18. Thecompression collar of claim 16, wherein the compression collar includesno knitlines and no injection points from injection molding.
 19. Thecompression collar of claim 16, further comprising flat surfaces on theinner periphery of the bore of the compression collar that are parallelto a central axis of the compression collar such that the flat surfacesare configured to be tangent to a radially-outward facing surface of thepipe around which the compression collar is received.
 20. Thecompression collar of claim 19, wherein the removed opening includespositioning tabs and there are as many flat surfaces on the innerperiphery as there are positioning tabs.
 21. The compression collar ofclaim 16, wherein the compression collar further comprises a supportingextension for reinforcing the piping past the fitting, the supportingextension being positioned on an axial end of the compression collaropposite the removed opening.
 22. The compression collar of claim 21,wherein the supporting extension tapers as it extends away from theopening.
 23. The compression collar of claim 16, further comprising achamfered edge in the bore at the axial end of the bore that is oppositethe axial end having the removed opening.
 24. The compression collar ofclaim 16, further comprising a curved corner with a radius of curvatureat the axial end of the bore that is opposite the axial end having theremoved opening.
 25. The compression collar of claim 16, wherein theinner periphery of the removed opening includes at least one positioningtab in which the at least one positioning tab is configured to axiallyposition the compression collar on an end of a pipe.
 26. The compressioncollar of claim 25, wherein the at least one positioning tab includes aplurality of positioning tabs.
 27. The compression collar of claim 16,wherein the removed opening has an inner periphery with a profile inaxial cross section that matches, in part, an adjacent profile in axialcross section of an inner periphery of the bore and with a non-matchingpart of the profiles defining at least one positioning tab in the innerperiphery of the removed opening.